In recent years, an increased concern for the energy saving measures has led to an active development of the infrared shielding film to block the transmission of heat rays in the sunlight entering through the window glass of a building and a vehicle. This makes it possible to reduce the load on the cooling facilities so as to be an effective energy saving measure.
Hitherto, a proposal is disclosed in which a laminated film formed by alternately laminating a high refractive index layer and a low refractive index layer as the infrared shielding film is fabricated by a dry film forming method such as a vapor deposition method or sputtering. In addition, it is also known that the laminated film can be designed so as to reflect visible light instead of near infrared light by adjusting the optical film thickness of the laminated film formed by the alternate lamination.
However, the dry film forming method has problems that the manufacturing cost is high, it is difficult to manufacture a large area film, and the method is limited to a heat resistant material.
Hence, a method using a thermosetting resin (JP 8-110401 A) and a method using a UV curing resin (JP 2004-123766 A) are disclosed as the method to fabricate the film by a coating method. These methods are advantageous in respect of the manufacturing cost, a large area and the like but undesirable in respect of the environmental conservation since both of them are a method using a large amount of organic solvents. Therefore, the water-based coating is preferable for the manufacture of the film and a water-soluble polymer capable of being coated by the water-based coating is preferable as the resin used in the coating liquid from the viewpoint of such environmental conservation. For example, an infrared shielding film is disclosed in WO 2012/014607 A which is formed of a refractive index layer containing a polyvinyl alcohol of a water-soluble polymer and a metal oxide.
Incidentally, there are a sequential coating to laminate the layers by coating and drying one by one and a simultaneous multilayer coating to coat a plurality of layers at the same time as a general method to fabricate a laminated film by coating two or more layers on a substrate. There are spin coating, bar coating, blade coating, and gravure coating as the sequential coating, but the productivity by the sequential coating is low since the number of coating and drying increases in the case of fabricating a multilayer film such as an optical reflective film. On the other hand, there is a method using curtain coating or slide bead coating as the simultaneous multilayer coating, and the productivity by the method is high since a plurality of layers can be formed at the same time.